[dk-tug] Undefined references

Hvorfor kan jeg få referencen frem til label'en i nedenstående? Det
virkede, da jeg lavede det for et par år siden, men nu får jeg følgende
besked: "LaTeX Warning: There were undefined references.", og referencen
fremstår som (??).

Poul Riis


\documentclass[a4paper,oldfontcommands,article,oneside]{memoir}
\usepackage[ansinew]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[danish]{babel}
\usepackage[leqno,fleqn,intlimits]{amsmath}
\usepackage[intlimits]{amsmath}
\usepackage{amssymb}
\usepackage{enumitem}
\usepackage[amsmath,thmmarks]{ntheorem}
\usepackage[ntheorem,overload]{empheq}
\usepackage{multido}
\usepackage[dvips,svgnames,x11names]{xcolor}
\usepackage{pst-fr3d}
\usepackage{pstricks-add}
\usepackage{datetime}
\usepackage{csquotes}


\topmargin=-0.5cm \textwidth=16.5cm
\textheight=24.5cm \hoffset=-2cm
\tolerance=5000 \hbadness=5000
\pretolerance=2500
\parindent=0em

\DeclareMathSymbol{\C}{\mathalpha}{AMSb}{"43}
\DeclareMathSymbol{\N}{\mathalpha}{AMSb}{"4E}
\DeclareMathSymbol{\Q}{\mathalpha}{AMSb}{"51}
\DeclareMathSymbol{\R}{\mathalpha}{AMSb}{"52}
\DeclareMathSymbol{\Z}{\mathalpha}{AMSb}{"5A}


\theoremheaderfont{\normalfont\bfseries\color{Blue4}}
\theorembodyfont{\normalfont\color{Blue4}}
\theoremseparator{:}
\theoremstyle{break}
\theoremnumbering{arabic}
\newtheorem{eksempel}{Eksempel}

\theoremstyle{nonumberplain}
\theorembodyfont{\normalfont}
\theoremheaderfont{\normalfont\bfseries}
\theoremseparator{:}
\theoremsymbol{\enskip\ensuremath{\fcolorbox{Green3}{Cornsilk1}{q.e.d.}\hspace{3em}}}

\newtheorem{proof}{Bevis}

\newcommand\e{\mathrm{e}}

\makeatletter
\newcommand\dato{\two@digits{\the\day}.\two@digits{\the\month}.\two@digits{\the\year}}
\makeatother


\makepagestyle{pr}
\makeoddhead{pr}{\tiny Nogle typer første ordens differentialligninger, 
version \dato, \currenttime, PR}{}{}
\makeheadrule{pr}{\textwidth}{\normalrulethickness}
\makeoddfoot{pr}{}{\thepage{}/{}\thelastpage}{}

\pagestyle{pr}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\begin{empheq}[box=\colorbox{MistyRose1}]{equation}
Q(f(x))=H(x)+ c
\label{Qfx}
\end{empheq}
... man skal løse ligning \eqref{Qfx}....
\end{document}